[Changes in the duration of pauses between self-stimulations in response to cortisol]

Intraperitoneal administration of glucocorticoid hormone cortisol (10 mg/kg) decelerated the self-stimulation (SS) frequency within 5-7 min. The maximal effect occurred within 10 to 20 min. Histograms of pauses duration between SS revealed a shift of mean values from 2.0-2.5 to 4-6 sec. A sharp increase of long pauses transformed chiefly mono- modal forms of control histograms into bimodal those under the hormonal effect. Behaviourally this was manifested by occurrence of burst type of SS responses when series of uninterrupted instrumental responses alternated with prolonged pauses between them. The data obtained are considered from the stand-point of systemic approach to analysis of organization of willed behaviour and role of cortisol in central mechanisms of positive reinforcement.